Methiod of making cellulose acetate teixtile fibers by acetylization of relgenerated cellulose fibers



T XTILE, FIBERS BY ACETYLIZATION OF i -GENE RATED CELLULOSE FIBERS Takai, Tokyo, Japan,

Co., Ltd Tokyo, Japan, a corporation of Japan ,1 "-No Diiawing.Application May 14, 1953,

' Serial No. 355,150

F r j 3Claims. c1. 8-121 This invention relates to the preparation ofcellulose acetate fiber having an acetic acid content of at least 40% byvapor phase acetylation of cellulosic fibers while retaining the fiberstructure.

It has previously been proposed to acetylate cellulosilc fibers whileretaining their fiber structure by carrying out the acetylation both inliquid and vapor phase. However, it has hitherto been impossible toproduce a cellulose acetate fiber having an acetic acid content from4062% by weight (which corresponds approximately to cellulose diacetateor triacetate) free from discoloration and brittleness and having at thesame time a high tensile strength and low elongation. Directacetaylation of cellulose has hitherto generally been employedcommercially to produce only cellulose monoacetate fiber, while fibershaving a higher acetic acid content have been made commercially bycomplete acetylation followed by a dry spinning procedure involvingpartial hydrolysis to'reduce the acetic acid content. In the first case,the acetate fiber is a mere modification of ordinary cellulose fiberpossessing essentially the same chemical properties and dry afiinity asordinary cellulose. Dry spun cellulose acetate fiber on the other hand,even when the acetic acid content has been reduced to approximately thatof cellulose diacetate, possesses undesirably low tensile strength andhigh elongation.

One object of the present invention is to provide a cellulose acetatefiber having an acetic acid content corresponding approximately tocellulose diacet-ate and celluassignor to Toho Rayon States Patent itrast to the mechanically applied crimp of the thermoplastic fibers,originates in the fine inner structure of the fibers and is permanentthrough spinning, weaving, washing, ironing and other similar fabrictreatments, which makes such viscose fiber particularly valuable. Theper manent structural crimp of such viscose staple rayon is retainedthroughout the acetylation process of the present invention.

The invention may be applied to continuous cellulosic fibers which maybe lightly twisted together to form a yarn or rope prior to acetylation,or it may be applied to a mass of loose staple fibers which may beconveyed through the several steps of the process on a suitable belt orwire mesh conveyor, or the like. If desired, the lcellulosic fibers,either continuous or staple, may be loosely woven 1 or knitted to form afabric which may then be subjected to the acetylation process of thepresent invention.

The invention is characterized in that the cellulosic fiber isimpregnated with an acetylation catalyst from an aqueous solutionthereof, dried to remove at least a portion of the water content of theimpregnated fiber, treated with acetic acid vapor to replace and removethe residual Water content, then acetyl-ated with acetic acid anhydridein vapor form. The entire process is preferably carried out with thecellulosic fiber advancing continuously through each successive step,particularly the steps involvlose triacetate and having a high tensilestrength together with low elongation and essentially the same dyeingcharacteristics as dry-spun acetate fiber.

Another object is to provide a cellulose acetate fiber having apermanent structural crimp and having an acetic acid content from 4062%4055 by weight.

Still a further object is to provide a process for continuous vaporphase acetylation of cellulosic fibers while retaining the fibrousstructure of the lcellulosic material.

A further object is to provide a method for the vapor phase acetylationof celluosic fibers, particularly fibers of regenerated cellulose, whileretaining the fiber structure, without discoloration of the fibers.

Other and further objects will description which follows.

The present invention may be employed for the production of celluloseacetate fibers from a wide variety of cellulose fibers, includingcotton, regenerated cellulose and wood-pulpr However, .theinvention isparticularly be apparent from the by weight, preferably from r that isrequired for the acetylation reaction, it

ing treatment with acetic acid and with acetic anhydride.

Among the acetylation catalysts which are suitable for use in thepresent invention are salts, of which there are particularly preferredthe acetates such as potassium,

, sodium, or lithium acetates; the phosphates, such as see.-

sodium phosphate, tert.-sodium phosphate, the ammonium phosphates, etc.;the chlorides, such as zinc chloride, cupric chloride, aluminumchloride, stannous chloride, stannic chloride, etc.; the sulfates, suchas copper sulfate,

1 aluminum sulfate, zinc sulfate, alum, etc.; and the oxalates, such asammonium oxalate, ammonium acid oxalate, etc.; and mixtures of any twoor more of such salts.

The catalysts are preferably applied to the cellulosic fiber fromaqueous solution which may suitably contain from about 10-20% by weightof the desired salt. The fiber may be passed through a container filledwith the aqueous salt solution or the solution may be sprayed onto thefibers, the impregnation preferably being carried out at roomtemperature (although elevated temperatures a may be employed ifdesired) at which temperature a contact time of from about 10 to about60 minutes is employed to insure satisfactory impregnation of the fiber.The impregnated fiber, which contains about 515% by weight of thecatalyst, is then passed between squeeze rolls to remove excess Water,or it may be centrifuged if desired, and further dried in hot air.ordinarily has a water content at this point of from 40-75% by weight,usually from 55-65% by weight.

In order to minimize the quantity of acetic anhydride is preferred toreplace and remove the residual water content of the impregnated fibersfollowing the aforementioned drying operation by passing the fiberscontinuously through a The dried fiber closed chamber filled with aceticacid vapor and main- Patented Feb. 5, 1957 tained at a temperature of100 to 130 C., preferably at a temperature of 105 to 115 C. Removal andreplacement of residual water ordinarily is completed in from to 45minutes, the best results having been obtained in a period of about tominutes.

Immediately following the exposure to acetic acid vapor the fiber isadvanced into a separate chamber filled with acetic anhydride vapor andmaintained at about 100 to 140 C., preferably at about 110 to 130 C. Inorder to achieve the desired degree of acetylation the fiber must bemaintained in contact with acetic anhydride vapor for a period of atleast 3 hours, preferably from 4 to 7 hours, during which time thesupply of acetic anhydride vapor to the reaction chamber-is constantlyrenewed. The acetic 'acid present in the fiber as it is introduced intothe acetylation chamber together with the acetic acid formed duringacetylation reaction is constantly withdrawn along with the excessacetic anhydride vapor. The mixture-is condensed and then distilled in aconventional stainless steel plate column to separate the anhydride fromthe acid. The anhydride is then recirculated to the acetylation chamber.

The acetylated fiber is continuously withdrawn from the acetylationchamber through a restricted opening, washed with water, oiled anddried.

The cellulose acetate fiber of the present invention-has unexpectedlyexcellent physical properties as compared with the convential dry-spunacetate fibers, having a dry tensile strength of at least 1.70gram/denier, a wet tensile strength of at least 1.30 gram/denier, a looptensile strength of at least 1.25 gram/denier, whilehaving an ultimateelongation no greater than about 25% (dry) and about 22% (Wet). Thephysical properties of the preferred fibers of the present inventionhaving an acetic acid content of 55% by weight are even better. The dyeafiinity of the acetate fibers of this invention, on the other hand, issubstantially the same as that of dry-spun acetate fiber, the fibersbeing dyed with celliton color and not with direct dyes, whereascellulose monacetate fibers made by fibrous acetylation are dyed withdirect color and not with celliton color. In addition, the acetatefibers of the present invention have a lower moisture regain (not over7.5%) than cellulose monoacetate fibers.

The following specific examples are given by way of illustration and arenot intended as a limitation upon the scope of the invention.

Example I Viscose rayon staple fiber having a permanent structural crimp(6.8 per cm.) is immersed in an aqueous solution containing about 15%sodium acetate for an hour at room temperature. The fiber is thendehydrated in a centrifuge to reduce the water content to approximately100% of the weight of the fiber, the amount of catalyst contained in thefiber being then about 10% by weight of the fiber. The fiber is thenpicked and further dried in hot air to approximately 60% water content.The loose fiber is then placed on a wire mesh conveyor belt on which itis carried through a closed chamber maintained at about 110 C. andfilled with acetic acid vapor at atmospheric pressure, the time ofexposure of the fibers to the acid vapor being approximately 30 minutes.The fiber comes out of the acid chamber through a slit and is thenadvanced through a slit into a second closed chamber filled with aceticanhydride vapor at atmospheric pressure, the second chamber beingmaintained at a temperature of about 130 C. The fiber is allowed toremain in the second chamber for about five hours in order to reach thedesired degree of acetylation, the acetic anhydride being vaporized fromthe lower portion of the chamber from a constantly renewed supply. Theacetic acid car tied into this chamber on the fibers, together with anyacetic acid formed during the acetylation reaction is constantly removedfrom the chamber along with excess acetic anhydride vapor. The mixedvapors are then con- Example 11 Spun-dyed viscose staple fiber having ap :rmanent structural crimp is treated as described in Exam le I, exceptthat an aqueous solution of potassium acetat is used in place oi thesodium acetate solution, the am cunt of catalyst contained in the fiberbeing about 8% b v weight of the fiber. The chamber containing aceticanhy ride is maintained at a ternperature of 120 C. and the tit exposureof the fiber to the acetic anhydride vapors i hours. The resultingproduct has an acetic acid con of 53%,the acetylated fiber'having thesame permane structural crimp as the original viscose staple fibers. Thecolor of the original dyed viscose staple may be black, blue, brown,orange, yellow, navy blue, pink, purple, red, or any other color and theshade of these colors is not changed by the acetylation procedure.

Example 111 Example IV Spun-dyedviscose rayon yarn made from fibershaving a permanent structural crimp is treated as described in ExampleLexcept that 12% amonium oxalate based on the weight of the ,yarn isemployedas the catalyst. The resultingcellulose acetateyarn possessesthe same color and crimped :fibrous structure as the original viscoserayon yarn and has an acetic acid content of 49%.

Example V Example VI Fabric woven from spun-dyed viscose rayon staplefiber having a permanent structural crimp is treated as described inExample 1, except that tertiary sodium phosphate is employed ascatalyst, the acetylation being carried out at -130 C. for five hours.The resulting cellulose acetate fabric possesses the same color andcrimped fibrous structure as the original and has a 50% acetic acidcontent.

Example VII Viscose rayon staple fibers having a permanent structuralcrimp are treated as described in Example I, except that the acetylationis carried out for four hours at C. The resulting cellulose acetatefiber possesses the same crimped fibrous structure as the original fiberand has a 42% acetic acid content.

The superiority of the cellulose acetate fiber of the present inventionas compared to cellulose monoacetate made by fibrous acetylation ordry-spun acetylated fiber made by complete acetylation followed bypartial hydrolysis is shown in the following table:

vapor at 100-140' C. for a period of at least three hours.

2. The method as defined in claim 1 in which said re- Monoacetate fiberProducts of the present Dry-spun aceinventlon tats fiber Acetic a idcontent (percent).- 61 53.

Tensilelgltrength (d1"y),g. 1.80 1.48.

Tensile strength (wet), g./d. 1.38 0.82.

Tensile grztrenglthfloop), gt./d 183% on ati 'm ercen g y p 19.9 22.7.-.28.0.

Same as dry-spun cellulose Dyed with cel- Dyed with direct coloracetate. Dyed with celliliton color and. and not with celliton ton colorand not with not; with direct color. direct color. color.

Moistur regain (percent) 9.5 7.5. 5. 6.4.

Numba of crimp per cm 6.8 (permanent 7.4 (mechanical structural crimp).crunp).

Crimp elasticity (percent) 69.8... 65.5.

It is apparent from the foregoing data that the fiber of the presentinvention diifers in chemical structure and dyeing properties from themonoacetate fiber, being in these respects closely similar to thedry-spun acetate fiber, but possesses remarkably superior physicalproperties as compared to the dry-spun acetate fiber.

The process of the present invention makes it possible to producecellulose acetate fibers having the same fiber structure as the startingmaterial and having an acetic acid content approximately equal tocellulose diacetate or triacetate (40-62% by weight) withoutdiscoloration or staining of the fiber and without embrittlement. Theinvention also makes possible the production of such cellulose acetateproducts in a continuous process using a relatively small amount ofacetylation catalyst without the necessity for carrying out theacetylation step at reduced pressures. Moreover, the fibers of thisinvention may be produced in the form of a loose mass, lap or roving,which, because of the excellent physical properties of the fibers, isadmirably adapted for further processing into yarns, threads, and wovenor knitted fabrics, or they may be produced in the finished form ofyarns, threads, and woven or knitted fabrics directly from correspondingcellulosic yarns, etc. without loss of fibrous structure.

Although I have herein described specific embodiments of my invention, Ido not intend to limit myself solely thereto, but to include all of theobvious variations and modifications within the spirit and scope of theappended claims.

I claim:

1. The method of making cellulose acetate textile fibers which comprisesimpregnating regenerated cellulose fibers with 5% to by Weight of anacetylation catalyst salt from an aqueous solution thereof, drying saidimpregnated fibers to remove a portion of the Water from saidimpregnated fibers, replacing completely the residual water in saidfibers with acetic acid by maintaining said fibers in contact withacetic acid vapor at 100-130 C. for a period from 10 to 45 minutes andsubsequently acetylating said fibers to an acetic acid content from 40%to 62% by weight while retaining their fibrous form by maintaining saidfibers in contact with acetic anhydride generated cellulose fibers arein the form of a loose mass of viscose rayon staple fibers having apermanent structural crimp.

3. The method of acetylating viscose rayon staple textile fibers havinga permanent structural crimp which comprises impregnating said fiberswith an acetylation salt catalyst from an aqueous solution containingabout 10% to 20% of said catalyst to provide impregnated fiberscontaining about 5% to 15% of said catalyst by weight of the fibers,drying said impregnated fibers to reduce the water content thereof to40% to by weight, passing said fibers continuously through a chambermaintained at 130 C. and filled with acetic acid vapor with said fibersin contact with said acetic acid vapor for 10 to 45 minutes until theresidual water in said fibers has been completely replaced with aceticacid, and subsequently passing the fibers continuously through a chambermaintained at -130 C. and filled with acetic anhydride vapor, the periodof contact between said fibers and acetic anhydride vapor being three toseven hours, and continuously removing acetic acid vapor and excessacetic anhydride vapor from said lastnamed chamber until there isproduced cellulose acetate fibers having a permanent structural crimp,an acetic acid content from 40% to 62% by weight, a dry tensile strengthof at least 1.70 gram/denier, and a wet tensile strength of at least1.30 gram/ denier.

References Cited in the file of this patent UNITED STATES PATENTS1,823,350 Clark et a1. Sept. 15, 1931 1,861,320 Rheiner May 31, 19321,926,498 Rheiner Sept. 12, 1933 2,253,724 New et al Aug. 26, 1941FOREIGN PATENTS 263,938 Great Britain Jan. 6, 1927 264,937 Great BritainJan. 31, 1927 755,267 France Sept. 4, 1933 OTHER REFERENCES MatthewsTextile Fibers, 5th ed., May 1947, pages 800, 822, 825.

Textile World, September 1949, pages 111-130.

1. THE METHOD OF MAKING CELLULOSE ACETATE TEXTILE FIBERS WHICH COMPRISESIMPREGNATING REGENERATED CELLULOSE FIBERS WITH 5% TO 15% BY WEIGHT OF ANACETYLATION CATALYST SALT FROM AN AQUEOUS SOLUTION THEREOF, DRYING SAIDIMPREGNATED FIBERS TO REMOVE A PORTION OF THE WATER FROM SAIDIMPREGNATED FIBERS, REPLACING COMPLETELY THE RESIDUAL WATER IN SAIDFIBERS WITH ACETIC ACID BY MAINTAINING SAID FIBERS IN CONTACT WITHACETIC ACID VAPOR AT 100* -130* C. FOR A PERIOD FROM 10 TO 45 MINUTESAND SUBSEQUENTLY ACETYLATING SAID FIBERS TO AN ACETIC ACID CONTENT FROM40% TO 60% BY WEIGHT WHILE RETAINING THEIR FIBROUS FORM BY MAINTAININGSAID FIBERS IN CONTACT WITH ACETIC ANHYDRIDE VAPOR AT 100* -140* C. FORA PERIOD OF AT LEAST THREE HOURS.